2.1. Introduction to Configuration Planning

Configuration planning involves making decisions about how you plan to use the Linux FailSafe cluster, and based on that, how the disks and interfaces must be set up to meet the needs of the highly available services you want the cluster to provide. Questions you must answer during the planning process are:

• What do you plan to use the nodes for?

  Your answers might include uses such as offering home directories for users, running particular applications, supporting an Oracle database, providing Netscape World Wide Web service, and providing file service.

• Which of these uses will be provided as a highly available service?

  To offer applications as highly available services that are not currently available as Linux Failsafe software options, a set of application monitoring shell scripts needs to be developed that provides switch over and switch back functionality. Developing these scripts is described in the Linux FailSafe Programmer's Guide. If you need assistance in this regard, contact SGI Global Services, which offers custom Linux FailSafe agent development and HA integration services.

• Which node will be the primary node for each highly available service?

  The primary node is the node that provides the service (exports the filesystem, is a Netscape server, provides the database, and so on) when the node is in an UP state.

• For each highly available service, how will the software and data be distributed on shared and non-shared disks?

  Each application has requirements and choices for placing its software on disks that are failed over (shared) or not failed over (non-shared).

• Are the shared disks going to be part of a RAID storage system or are they going to be disks in SCSI/Fibre channel disk storage that has mirroring such as the Linux Raid Tools implemented on them?

  For reliability, shared disks must be part of a RAID storage system or in SCSI/Fibre channel disk storage with mirroring on them.

• Will the shared disks be used as raw devices/volumes or as volumes with filesystems on them?

  Logical volumes, filesystems, and raw partitions are all supported by Linux Failsafe. The choice of volumes, filesystems, or raw devices depends on the application that is going to use the disk space.

• Which IP addresses will be used by clients of highly available services?

  Multiple interfaces may be required on each node because a node could be connected to more than one network or because there could be more than one interface to a single network.

• Which resources will be part of a resource group?

  All resources that are dependent on each other have to be in the resource group.

• What will be the failover domain of the resource group?

  The failover domain determines the list of nodes in the cluster where the resource group can reside. For example, a volume resource that is part of a resource group can reside only in nodes from which the disks composing the volume can be accessed.

• How many highly available IP addresses on each network interface will be available to clients of the highly available services?

  At least one highly available IP address must be available for each interface on each node that is used by clients of highly available services.

• Which IP addresses on primary nodes are going to be available to clients of the highly available services?

• For each highly available IP address that is available on a primary node to clients of highly available services, which interface on the other nodes will be assigned that IP address after a failover?

  Every highly available IP address used by a highly available service must be mapped to at least one interface in each node that can take over the resource group service. The highly available IP addresses are failed over from the interface in the primary node of the resource group to the interface in the replacement node.

As an example of the configuration planning process, say that you have a two-node Linux FailSafe cluster that is a departmental server. You want to make four XFS filesystems available for NFS mounting and have two Netscape FastTrack servers, each serving a different set of documents. These applications will be highly available services.

You decide to distribute the services across two nodes, so each node will be the primary node for two filesystems and one Netscape server. The filesystems and the document roots for the Netscape servers (on XFS filesystems) are each on their own striped LVM logical volume. The logical volumes are created from disks in a RAID storage system connected to both nodes.

There are four resource groups: NFSgroup1 and NFSgroup2 are the NFS resource groups, and Webgroup1 and Webgroup2 are the Web resource groups. NFSgroup1 and Webgroup1 will have one node as the primary node. NFSgroup2 and Webgroup2 will have the other node as the primary node.

Two networks are available on each node, eth0 and eth1. The eth0 interfaces in each node are connected to each other to form a private network.

The following sections help you answer the configuration questions above, make additional configuration decisions required by Linux FailSafe, and collect the information you need to perform the configuration tasks described in Chapter 3, and Chapter 5.